Our long-term objective is to understand the molecular mechanisms operative in the development and differentiation of T- lymphocytes. T-cell acute lymphoblastic leukemias (ALL) serve as a good model system to study the regulation of gene expression during T-cell differentiaton. Using leukemic cells and recently available molecular probes, we will analyze the expression and arrangement of T-cell specific genes whose expression occurs at different times during T-cell ontogeny. We will examine (i) the rearrangements of antigen-specific T-cell receptor (TCR) genes alpha, beta, and gamma by Southern blot analysis; (ii) expression of TCR genes as well as genes for the surface antigens T3 and T11 at the transcriptional level by Northern blot analysis, and (iii) the cytoplasmic appearance of T11 and T3 proteins with appropriate monoclonal antibodies. These analyses should enable us to identify new stages in T-cell differentiation and should provide insight into the ontological development of T-lymphocytes. Such information will then be used clinically to, (a) determine T-cell lineage, (b) classify leukemias, (c) examine the origin of leukemias, and (d) determine the extent of minimum residual disease. This molecular approach has considerable potential for broadening the scientific basis for the classification and diagnosis of lymphoid leukemias and may provide a very sensitive and accurate measure of therapy as well as an earlier warning of impending relapse in T-cell ALL patients. Alteration in the structure of proto-oncogenes can be brought about through the process of chromosomal translocation. Translocation can alter the expression of these genes which may contribute to the leukemic transformation. We will analyze translocation in T-cell ALL that may have breakpoints in beta gene of TCR. Alteration in the structure of beta gene will identify one of the two genes affected by the translocation and provide a probe for cloning and characterzation of the second gene. This information should provide insight into mechanism(s) of protooncogene activation and thus their potential role in the oncogenic process.